1. Field of the Invention
The present invention relates to semiconductor wafer testing and, more particularly, to determining the generation lifetime of a product semiconductor wafer.
2. Description of Related Art
Metallic contamination is an important issue in the fabrication of metal-oxide-semiconductor (MOS) devices. This contamination can come from a number of sources including pre-clean operations, diffusion and oxidation processes, process gases and processing equipment such as ion implanters. Metallic contamination lowers the carrier generation lifetime and is generally an important concern with indirect bandgap semiconductors such as silicon.
Reduced generation lifetime has an adverse effect on junction leakage currents and memory storage times. Conventionally, monitor wafers are used to measure generation lifetime. However, this is becoming increasingly undesirable due to the cost of processing and the cost of monitor wafers. Additionally, the generation lifetime measured is that associated with SHR (Shockly-Hall-Read) generation within the space charge region which is near the surface where devices are made. Recombination lifetime is sensitive to a wide variety of metallic contaminants located over about half of the bandgap. However, it does not locally access the semiconductor quality near the surface where actual devices are made.
Accordingly, what is needed is a method and apparatus for measuring generation lifetime in the near surface region of a semiconductor wafer where devices are made. It is also desirable to make these measurements on product semiconductor wafers having a pattern of integrated circuits formed thereon with scribe lines separating the integrated circuits from one another.